The present invention is directed to a method for controlling beet armyworm (Spodoptera exigua) and other Lepidopteran pests on a genetically altered cotton plant whose genome makeup includes a gene derived from Bacillus thuringiensis (Bt). More specifically, when applied to plants which express a microbially derived protein toxic to certain insect species, activity of pesticides of structural formula (I) below, is markedly enhanced against other insects.